It has previously been proposed to seal beverage preparation ingredients in individual air-impermeable packages. For example, cartridges or capsules containing ground coffee are known for use in certain coffee preparation machines which are generally termed “espresso” machines. In the production of coffee using these preparation machines the coffee cartridge is placed in a brewing chamber and hot water is passed though the cartridge at relatively high pressures, thereby extracting the aromatic coffee constituents from the ground coffee to produce the coffee beverage.
In EP-A-1440903 a cartridge is described which is formed from high density polyethylene, polypropylene, polystyrene, polyester, or a laminate of two or more of these materials. The cartridge has an inlet for the introduction of water into the cartridge, and an outlet for a beverage produced from said the beverage ingredients. The cartridge comprises an outer member, an inner member inserted in the outer member and an aperture in a beverage flow path linking the inlet to the outlet for producing a jet of the beverage. The cartridge produces a jet of the beverage which can be used to alter the appearance and characteristics of the dispensed beverage, by for example entraining air into the jet of beverage to produce a multitude of small air bubbles in the dispensed beverage.
The quality of many beverage ingredients, in particular coffee, starts deteriorating when exposed to the air, for example due to oxidisation of fatty acids and evaporation of volatile oils which contribute to the flavour of the beverage. This causes the coffee to have a stale flavour. In order to maintain the quality of the beverage ingredients and to give the cartridges a reasonable shelf life, it is therefore important to prevent the ingress of air and moisture. Thus, whilst the materials used in the manufacture of the cartridges are generally impermeable to liquids, to protect them from air penetration, such cartridges are often packaged in gas impermeable secondary packaging, such as plastic wrappers or metallised foils. Suitable materials used in such packaging are, for example, polyamide coated cellulose film, ethylene vinyl alcohol polymers (EVOH) or other vinyl alcohol polymers (PVOH).
However, the use of secondary packaging has the disadvantage that, once it has been opened, the cartridges are vulnerable to air ingress which causes staling of the product. In addition, it is highly desirable to reduce the amount of packaging used, both in terms of reduction of waste products which need to be disposed of and to reduce packaging costs. Furthermore, it is neither cost effective, nor environmentally friendly, to wrap each cartridge separately.
A number of prior art containers and packages exist, especially for food products, which are gas and water impermeable. For example U.S. Pat. No. 5,819,507 describes a packaging container used for a liquid food formed from a multilayer resin sheet, such as polypropylene and ethylene-vinyl alcohol polymer, polystyrene and ethylene-vinyl alcohol polymer, polyethylene and polystyrene. The sheet is formed by co-extrusion melding or blown film melding deformed into a cylindrical container, which is bonded to a separately formed sleeve or expanded polypropylene or another material of greater rigidity than the resin sheet.
As described in U.S. Pat. No. 6,387,423 a composite sheet can be preformed, for example of polypropylene and ethylene-vinyl alcohol polymer, and the food product wrapped in the sheet and heat sealed.
Whilst the packaging materials described above are highly suitable for protecting the beverage ingredients contained in the cartridges described above, because of their complex shape, the formation of the component parts of the cartridges adds a limitation as to how these materials can be used. The afore-mentioned cartridges are designed to incorporate a variety of features that are not possible with a part formed from sheet material.
It is therefore desirable to retain the present general construction of the cartridges described in EP-A-1440903, whilst making them substantially gas and water impermeable.
Such cartridges are conveniently formed by an injection moulding process, which is one of the most common methods used in manufacturing plastic articles and components for a wide variety of applications. Although tooling is expensive, the cost per part is low and the process is particularly suitable for accurate high volume production of parts which require a high tolerance.
In order that the outer member of the cartridge has sufficient strength and rigidity to maintain its shape and not deform in use, and can be injection moulded, it is necessary to use a suitable polymer such as polypropylene, polyethylene or polystyrene. However whilst these materials are impermeable to liquid, they are not sufficiently impermeable to gases and it is desirable to include a gas impermeable barrier layer, such as ethylene-vinyl alcohol (EVOH) polymer.
Whilst it is possible to form multilayer laminates of different materials, using thermoforming and other processes, the options have hitherto been somewhat limited with injection moulding. Co-injection moulding is a process in which two different materials, such as polymers, are formed into a laminar structure during injection moulding. This produces a sandwich construction of a skin and an inner core. However until recently the polymers used have had to be compatible in so far as they melt at the same temperature and bond together. If the layers are not bonded, the sandwich tends to delaminate, i.e the layers physically separate, due to differential shrinkage.
With recent advances in co-injection techniques, however, it has become possible to mould multi-layer polymer articles using a sandwich consisting of a core enclosed by inner and outer layers in which the materials used for the core and inner/outer layers are different. This means that the core may be formed from a gas impermeable material, such as EVOH, whilst the inner/outer layers may be formed from a more cost effective material such as polyethylene, polypropylene etc. A method of co-injection moulding multi-layer polymer articles is described in WO-A-02/081172.
One of the disadvantages of injection moulding are that the parts to be moulded (and therefore the injection mould itself) must be designed carefully to ensure that the mould can be properly filled, that the finished part can be extracted and that a myriad of other problems are avoided, such as distortion, stress failure and cracking. With an article having a complex geometry, as is required for these cartridge component parts, and the requirement for rigidity as well as impermeability, this has not been hitherto possible to achieve.
However the complexity of the design of the cartridge component parts brings a further significant challenge in co-injection moulding, which is currently generally only used for manufacturing articles having simple, axially symmetric shapes, such as cups and tubs. The structure of a more complex article, for example one which is asymmetric and has ribs and section changes as in the afore-mentioned cartridges component parts, causes turbulence in the plastic flow during the injection process and disrupts the laminar flow required to maintain a contiguous core layer. This results in an uncontrolled layer structure which compromises the uniformity of the core layer. The resulting moulded articles therefore have a structure and layer thickness which cannot be relied on to function as intended, which is particularly disadvantageous where the core layer is intended to be a barrier layer or a uniform coloured layer. This can also cause problems when sealing to a face of a co injected part. It is possible for the inner material to come so close to the outside of the part that the physical strength of any supplementary sealing or welding process would be insufficient for its function.
EP-A-0735943 addresses the problem of co-injection moulding articles having a complex shape by designing the mould cavity so that the flow paths therein all have substantially the same hydraulic resistance. In addition the injection points are selected and the injection temperature, pressure and flow rate are controlled so that the different flows of injected materials meet each other in a fluid condition at a predetermined point.
It is an object of the present disclosure to further improve the method and apparatus for co-injection moulding multilayered articles having a complex shape.